Wireless sensor device

ABSTRACT

A wireless sensor device capable of constant operation without replacement of batteries. The wireless sensor device is equipped with a rechargeable battery and the battery is recharged wirelessly. Radio waves received at an antenna circuit are converted into electrical energy and stored in the battery. A sensor circuit operates with the electrical energy stored in the battery, and acquires information. Then, a signal containing the information acquired is converted into radio waves at the antenna circuit, whereby the information can be read out wirelessly.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a wireless sensor device having aso-called sensing function, which is capable of reading out informationwithout contact, e.g., by radio communication. In particular, theinvention relates to a wireless sensor device which is used while beingimplanted in, swallowed by, or attached to the living body.

2. Description of the Related Art

Nowadays, an increasing number of information is being processed withthe development of IT technology. Among them is the informationmanagement for human health. For example, health checkups are regularlyconducted at companies, schools, and the like; individuals are informedof their heath conditions at least once or twice a year. When thecondition of one's health is not good, he/she will be noticed of thefact and receives treatment at a hospital.

Also, simple health measurement instruments for domestic use have beendeveloped for easy checkups of one's health conditions. In recent years,portable measurement instruments have also become widespread,contributing to early detection of diseases.

Reference 1 (Japanese Published Patent Application No. 2004-121632) isone of the examples of the heath measurement instrument.

Reference 1 discloses a portable blood-pressure measurement instrument.Using such a measurement instrument, one can easily know his/her healthcondition.

However, the conventional health measurement instrument disclosed inReference 1 has the following problems: even though the size of thehealth measurement instrument is reduced to some extent, it is stilllarge for being carried around. Moreover, even when a user acquiresinformation with the measurement instrument, he/she may be unconsciousof a change in physical condition because the information cannot beimmediately seen by a medical specialist. This could result in aprogression of disease,

In view of the foregoing, a semiconductor device having a function ofwirelessly acquiring physical information has been devised, for exampleby attaching a sensor device having a radio function to a human body. Aspecific example thereof is disclosed in Reference 2 (Japanese PublishedPatent Application No. 2006-99757). In this example, physicalinformation in particular can be acquired with a dedicated wirelessreader device without the help of medical institutions and the like.

SUMMARY OF THE INVENTION

However, the wireless sensor device disclosed in Reference 2 is apassive type and operates only when there is a wireless signal supplyfrom outside. Thus, the wireless sensor device cannot operate when thereis no wireless signal supply from outside. Therefore, this device is noteffective in constantly acquiring physical information.

Meanwhile, the above-described problems can be solved by forming thewireless sensor device to be an active device and building a batteryinto the device. However, when the wireless sensor device is implantedin or swallowed by the body, the battery cannot be replaced easily.Furthermore, there is another problem in that the wireless sensor devicebecomes inactive when the battery runs out of charge.

In view of the foregoing problems, it is an object of the invention toprovide a wireless sensor device capable of constant operation withoutreplacement of batteries.

According to the invention, a wireless sensor device is equipped with arechargeable battery and the battery is recharged wirelessly.Specifically, the wireless sensor device of the invention includes anantenna circuit for transmission and reception of radio waves, a batteryfor storing electrical energy obtained from the radio waves, and asensor circuit for acquiring (sensing) information.

Radio waves received at the antenna circuit are converted intoelectrical energy, and the electrical energy is stored in the battery.The sensor circuit operates with the electrical energy stored in thebattery, and acquires information. Then, a signal containing theinformation acquired is converted into radio waves at the antennacircuit, whereby the information can be read out wirelessly.

Note that a memory circuit may be used to temporarily store theinformation acquired. In that case, by converting the information storedin the memory circuit into radio waves at the antenna circuit, theinformation can be read out wirelessly.

In the case of using the wireless sensor device of the invention in theliving body, radio waves transmitted from outside of the body areconverted into electrical energy at the antenna circuit so that theelectrical energy is stored in the battery. The sensor circuit operateswith the electrical energy stored in the battery, and acquires physicalinformation. Physical information means information that can serve as anindicator of the health condition of the living body. Typical examplesof physical information include blood pressure, heart rate, bodytemperature, respiration rate, the amount of gas in the blood, the valueof action current such as an electrocardiogram or anelectroencephalogram, blood glucose level, an internal image of thebody, and the like.

It is acceptable as long as a sensor used for the sensor circuit isselected in accordance with the physical information to be acquired.Further, by providing a plurality of sensor circuits in a wirelesssensor device, a plurality of kinds of physical information can beacquired.

The physical information acquired is stored in the memory circuit. Then,by converting the physical information stored in the memory circuit intoradio waves at the antenna circuit, the physical information can be readout wirelessly.

The wireless sensor device of the invention can be used not only foracquisition of physical information of the living body, but also forconstant acquisition of information in areas where it is difficult toacquire information by contact.

As described above, according to the invention, a wireless sensor devicecan be supplied with electrical energy without contact. Therefore,replacement of batteries is not necessary.

In the case of using the wireless sensor device in the living body, thebattery can be recharged without contact, without hurting the livingbody, while the wireless sensor device is being placed in the livingbody. By using electricity stored in the battery, the wireless sensordevice of the invention can constantly acquire physical information.

Physical information acquired by the wireless sensor device can betransmitted wirelessly. Therefore, the physical information can bemanaged with IT technology to be utilized for early detection ortreatment of diseases and the like.

The wireless sensor device of the invention can be widely used as adevice that can constantly acquire information not only in the livingbody but also in areas where it is difficult to acquire information bycontact. For example, the wireless sensor device can be utilized forsensing in areas where access of humans is limited such as a radiationcontrolled area.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a block diagram illustrating the configuration of a wirelesssensor device of the invention;

FIG. 2 illustrates application of the invention to a human body;

FIGS. 3A and 3B are block diagrams illustrating the configurations of anantenna circuit and a rectifier circuit, respectively, of a wirelesssensor device of the invention;

FIG. 4 is a block diagram illustrating the configuration of a wirelesssensor device of the invention;

FIG. 5 is a block diagram illustrating the configuration of a wirelesssensor device of the invention;

FIG. 6 is a cross-sectional view of a wireless sensor device of theinvention;

FIG. 7 is a cross-sectional view of a wireless sensor device of theinvention;

FIG. 8 is a cross-sectional view of a wireless sensor device of theinvention;

FIG. 9 is a top view of a substrate of a wireless sensor device of theinvention;

FIGS. 10A and 10B illustrate an electric double layer capacitor;

FIGS. 11A and 11B illustrate an electric double layer capacitor;

FIG. 12 is a cross-sectional view of a thin-film secondary battery;

FIGS. 13A and 13B illustrate an embodiment of a photosensor;

FIG. 14 illustrates an embodiment of a pressure sensor;

FIGS. 15A to 15D illustrate a method of fabricating a wireless sensordevice of the invention;

FIGS. 16A to 16C illustrate a method of fabricating a wireless sensordevice of the invention;

FIGS. 17A and 17B illustrate a method of fabricating a wireless sensordevice of the invention;

FIGS. 18A and 18B illustrate a method of fabricating a wireless sensordevice of the invention;

FIG. 19 illustrates a method of fabricating a wireless sensor device ofthe invention;

FIGS. 20A to 20C illustrate a method of fabricating a wireless sensordevice of the invention;

FIGS. 21A to 21C illustrate a method of fabricating a wireless sensordevice of the invention;

FIGS. 22A and 22B illustrate a method of fabricating a wireless sensordevice of the invention; and

FIG. 23 illustrates the configuration of a wireless sensor device of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiment modes and embodiments of the invention will be hereinafterdescribed with reference to the accompanying drawings. Note that theinvention can be implemented in various different ways and it will beeasily understood by those skilled in the art that various changes andmodifications can be made in the invention without departing from thespirit and scope thereof. Therefore, the invention should not beconstrued as being limited to the description in the followingembodiment modes and embodiments. In the accompanying drawings, likeportions or portions having like functions are denoted by like referencenumerals, and repetitive description thereof will be omitted.

(Embodiment Mode 1)

Embodiment Mode 1 of the invention is shown in FIG. 1. FIG. 1illustrates a block diagram of the invention. A wireless sensor device100 includes an antenna circuit 101, an oscillation circuit 102, amodulation circuit 103, a demodulation circuit 104, a logic circuit 105,an AD converter circuit 106, a sensor circuit 107, a memory circuit 108,a rectifier circuit 109, a charging circuit 110, a battery 111, and astabilizing power supply circuit 112.

In the case of performing communication with a magnetic field, theantenna circuit 101 includes, as shown in FIG. 3A, a coiled antenna 301and a tuning capacitor 302. The rectifier circuit 109 includes, as shownin FIG. 3B, a diode 303, a diode 304, and a smoothing capacitor 305.However, the configurations of the antenna circuit 101 and the rectifiercircuit 109 are not limited to them. hi the case of performingcommunication with not a magnetic field but an electric field, theantenna does not need to be in a coiled form.

The operation of the wireless sensor device 100 in this embodiment modewill now be described. An AC signal received at the antenna circuit 101is half-wave rectified by the diodes 303 and 304, and then smoothed bythe smoothing capacitor 305. By this smoothed voltage, the chargingcircuit 110 is activated to charge the battery 111. As the battery 111,for example, a secondary battery, a high-capacity capacitor, or the likecan be used.

An output voltage of the battery 111 is stabilized by the stabilizingpower supply circuit 112, and the stabilized voltage is supplied to theoscillation circuit 102, the modulation circuit 103, the demodulationcircuit 104, the logic circuit 105, the AD converter circuit 106, thesensor circuit 107, and the memory circuit 108.

Signals communicated with an external device are transmitted throughcarrier modulation. Therefore, the wireless sensor device of theinvention should demodulate the modulated signals. Examples of thecarrier frequency include, but not limited to, 125 kHz, 13.56 MHz, 950MHz, and the like. In addition, examples of a modulation method include,but not limited to, amplitude modulation, frequency modulation, phasemodulation, and the like.

Upon input of an external radio wave, which is a signal requesting toactivate the sensor circuit 107, to the antenna circuit 101, the signalis demodulated by the demodulation circuit 104. The demodulated signalis processed by the logic circuit 105. When the input signal is anencoded signal, it is decoded in the logic circuit 105. For example,when the signal from the external transmitter has been encoded withmodified Miller codes, NRZ-L codes, or the like, the encoded signal isdecoded in the logic circuit 105. The decoded data is transmitted to theAD converter circuit 106 and the sensor circuit 107, whereby the ADconverter circuit 106 and the sensor circuit 107 are activated.

With the activated sensor circuit 107, the wireless sensor device 100can detect external information. External information herein includes,but not limited to, pressure, light, odor, sound, and the like. Thesensor circuit 107 has a function of converting such externalinformation into an electrical signal. The output of the sensor circuit107 is converted into a digital signal by the AD converter circuit 106.The output signal of the AD converter circuit 106 is processed by thelogic circuit 105. For example, the signal is encoded by the logiccircuit 105 when necessary. The output of the logic circuit 105 ismodulated by the modulation circuit 103 and then input to the antennacircuit 101. The modulation circuit 103 performs modulation by mixingthe output of the oscillation circuit 102 and the output of the logiccircuit 105. The signal input to the antenna circuit 101 is radiated asradio waves.

As the sensor circuit 107, for example, a pressure sensor, aphotosensor, an odor sensor, a sound sensor, and the like can be used,but the invention is not limited to these. The memory circuit 108 isused for storing information that has been sensed, and is preferablynonvolatile memory, but the invention is not limited to this. Even whenthe memory circuit 108 is volatile memory, it can function in the sameway as nonvolatile memory as long it can secure a power supply. Thememory circuit 108 can be, for example, SRAM, DRAM, flash memory,EEPROM, FeRAM, or the like.

A physical information acquisition system that uses the wireless sensordevice of the invention will be briefly described with reference to FIG.2. FIG. 2 is a schematic view of a physical information acquisitionsystem that obtains physical information of humans without contact. Thewireless sensor device 100 is placed inside the living body.Specifically, the wireless sensor device 100 may be either implanted inthe living body or swallowed by the living body so as to be placed in adigestive organ. The battery included in the wireless sensor device ofthe invention can, even when placed inside the living body, storeelectrical energy without contact with the use of radio waves.

Note that the wireless sensor device of the invention may be configuredsuch that the battery is charged not only in sensing operation butconstantly, i.e., even when sensing operation is not conducted. Withsuch a configuration, power that will be consumed for one sensingoperation can be surely secured by the battery even under the conditionof weak radio waves.

The use of the wireless sensor device of the invention is not limited tothe use inside the living body. That is, the wireless sensor device ofthe invention can also be used while being attached to the surface ofthe living body.

Radio waves are transmitted from an interrogator 200 to the wirelesssensor device 100. Upon reception of the radio waves, the wirelesssensor device 100 sends physical information, which has been acquired bythe sensor circuit 107 included in the wireless sensor device 100, backto the interrogator 200. The interrogator 200 is connected to aninformation system (not shown) which analyzes the physical informationacquired. In this manner, physical information of humans can be acquiredwithout carrying a bulky measurement instrument. Further, sinceinformation can be analyzed automatically, it is possible to preventprogression of disease, which would otherwise be caused by delay ofnotification.

(Embodiment Mode 2)

Embodiment Mode 2 of the invention is shown in FIG. 4. FIG. 4illustrates a block diagram of the invention. A wireless sensor device400 includes antenna circuits 401 and 402, the oscillation circuit 102,the modulation circuit 103, the demodulation circuit 104, the logiccircuit 105, the AD converter circuit 106, the sensor circuit 107, thememory circuit 108, the rectifier circuit 109, the charging circuit 110,the battery 111, and the stabilizing power supply circuit 112.

In this embodiment mode, the antenna circuit 401 for reception of powerand the antenna circuit 402 for reception of signals are provided,unlike Embodiment Mode 1. When a plurality of antenna circuits havingdifferent functions are selectively used in this manner, powertransmission and signal transmission can be conducted by using differentradio frequencies. For example, power transmission can be conducted withradio waves having a frequency of 13.56 MHz by utilizing a magneticfield, while signal transmission can be conducted with radio waveshaving a frequency of 950 MHz by utilizing an electric field. Byselectively using a magnetic field and an electric field in accordancewith the frequency, power can be transmitted only a short distance,while signal can be transmitted both short and long distances. If powertransmission is conducted with a radio frequency of 950 MHz, there is apossibility that high power is transmitted to a far place, which couldcause interference with signal reception of other wireless devices.Therefore, when the distance of power transmission can be short, it ispreferable to lower the frequency and use a magnetic field.

The operation of the wireless sensor device 400 in this embodiment modewill now be described. An AC signal received at the antenna circuit 401is half-wave rectified by the diodes 303 and 304 shown in FIG. 3B, andthen smoothed by the smoothing capacitor 305. By this smoothed voltage,the charging circuit 110 is activated to charge the battery 111. As thebattery 111, for example, a secondary battery, a high-capacitycapacitor, or the like can be used.

An output voltage of the battery 111 is stabilized by the stabilizingpower supply circuit 112, and the stabilized voltage is supplied to theoscillation circuit 102, the modulation circuit 103, the demodulationcircuit 104, the logic circuit 105, the AD converter circuit 106, thesensor circuit 107, and the memory circuit 108.

Signals communicated with an external device are transmitted throughcarrier modulation. Therefore, the wireless sensor device of theinvention should demodulate the modulated signal. Examples of thecarrier frequency include, but not limited to, 125 kHz, 13.56 MHz, 950MHz, and the like. In addition, examples of a modulation method include,but not limited to, amplitude modulation, frequency modulation, phasemodulation, and the like.

A signal input to the antenna circuit 402 is demodulated in thedemodulation circuit 104. The demodulated signal is processed in thelogic circuit 105. When the input signal is an encoded signal, it isdecoded in the logic circuit 105. For example, when the signal from theexternal transmitter has been encoded with modified Miller codes, NRZ-Lcodes, or the like, the encoded signal is decoded in the logic circuit105. The decoded data is transmitted to the AD converter circuit 106 andthe sensor circuit 107, whereby the AD converter circuit 106 and thesensor circuit 107 are activated.

With the activated sensor circuit 107, the wireless sensor device 400can detect external information. External information herein includes,but not limited to, pressure, light, odor, sound, and the like. Thesensor circuit 107 has a function of converting such externalinformation into an electrical signal. The output of the sensor circuit107 is converted into a digital signal by the AD converter circuit 106.The output signal of the AD converter circuit 106 is processed by thelogic circuit 105. For example, the signal is encoded by the logiccircuit 105 when necessary. The output of the logic circuit 105 ismodulated by the modulation circuit 103 and then radiated as radio wavesfrom the antenna circuit 402. The modulation circuit 103 performsmodulation by mixing the output of the oscillation circuit 102 and theoutput of the logic circuit 105.

As the sensor circuit 107, for example, a pressure sensor, aphotosensor, an odor sensor, a sound sensor, and the like can be used,but the invention is not limited to these. The memory circuit 108 isused for storing information that has been sensed, and is preferablynonvolatile memory, but the invention is not limited to this. Even whenthe memory circuit 108 is volatile memory, it can function in the sameway as nonvolatile memory as long it can secure a power supply. Thememory circuit 108 can be, for example, SRAM, DRAM, flash memory,EEPROM, FeRAM, or the like.

Embodiment Mode 3)

Embodiment Mode 3 of the invention is shown in FIG. 5. FIG. 5illustrates a block diagram of the invention. A wireless sensor device500 includes the antenna circuit 101, the oscillation circuit 102, themodulation circuit 103, the demodulation circuit 104, the logic circuit105, the AD converter circuit 106, the memory circuit 108, the rectifiercircuit 109, the charging circuit 110, the battery 111, the stabilizingpower supply circuit 112, a CCD 501, and an LED 502.

In this embodiment mode, the wireless sensor device 500 includes the LED502 and the CCD 501, so that light emitted from the LED 502 illuminatesinside of the body and the CCD 501 shoots an image of the illuminatedobject. A light-emission source is not limited to the LED and othertypes of light emitter such as an EL element can also be used. Inaddition, the image pickup device is not limited to the CCD, and a CMOSsensor or the like can also be used, for example.

In the case of performing communication with a magnetic field, theantenna circuit 101 includes, as shown in FIG. 3A, the coiled antenna301 and the tuning capacitor 302. The rectifier circuit 109 includes, asshown in FIG. 3B, the diode 303, the diode 304, and the smoothingcapacitor 305. However, the configurations of the antenna circuit 101and the rectifier circuit 109 are not limited to them. In the case ofperforming communication with not a magnetic field but an electricfield, the antenna does not need to be in a coiled form.

The operation of the wireless sensor device 500 in this embodiment modewill now be described. An AC signal received at the antenna circuit 101is half-wave rectified by the diodes 303 and 304, and then smoothed bythe smoothing capacitor 305. By this smoothed voltage, the chargingcircuit 110 is activated to charge the battery 111. As the battery 111,for example, a secondary battery, a high-capacity capacitor, or the likecan be used.

An output voltage of the battery 111 is stabilized by the stabilizingpower supply circuit 112, and the stabilized voltage is supplied to theoscillation circuit 102, the modulation circuit 103, the demodulationcircuit 104, the logic circuit 105, the AD converter circuit 106, thememory circuit 108, the CCD 501, and the LED 502.

Signals communicated with an external device are transmitted throughcarrier modulation. Therefore, the wireless sensor device of theinvention should demodulate the modulated signal. Examples of thecarrier frequency include, but not limited to, 125 kHz, 13.56 MHz, 950MHz, and the like. In addition, examples of a modulation method include,but not limited to, amplitude modulation, frequency modulation, phasemodulation, and the like.

A signal input to the antenna circuit 101 is demodulated in thedemodulation circuit 104. The demodulated signal is processed in thelogic circuit 105. When the input signal is an encoded signal, it isdecoded in the logic circuit 105. For example, when the signal from theexternal transmitter has been encoded with modified Miller codes, NRZ-Lcodes, or the like, the encoded signal is decoded in the logic circuit105. The decoded data is transmitted to the AD converter circuit 106 andthe CCD 501, whereby the AD converter circuit 106 and the CCD 501 areactivated.

With the activated CCD 501, the wireless sensor device 500 can shoot anexternal image. While the CCD 501 is shooting an image, the LED 502 islighting. The output of the CCD 501 is converted into a digital signalby the AD converter circuit 106. The output signal of the AD convertercircuit 106 is processed by the logic circuit 105. For example, thesignal is encoded by the logic circuit 105 when necessary. The output ofthe logic circuit 105 is modulated by the modulation circuit 103 andoutput from the antenna circuit 101. The modulation circuit 103 performsmodulation by mixing the output of the oscillation circuit 102 and theoutput of the logic circuit 105. The memory circuit 108 is used forstoring information that has been sensed, and is preferably nonvolatilememory, but the invention is not limited to this. Even when the memorycircuit 108 is volatile memory, it can function in the same way asnonvolatile memory as long it can secure a power supply. The memorycircuit 108 can be, for example, SRAM, DRAM, flash memory, EEPROM,FeRAM, or the like.

As described above, using the image pickup device such as a CCD, thewireless sensor device of this embodiment mode can shoot an internalimage of the body. Thus, abnormality of inside of the body can bedetected at an early stage, which greatly contributes to maintainingone's health.

[Embodiment 1]

Embodiment 1 of the invention is shown in FIG. 6. FIG. 6 illustrates across section of the wireless sensor device of the invention. Thewireless sensor device shown in FIG. 6 includes a substrate 601, anantenna 602, a ferrite 603, a secondary battery 604, a flexible printedboard 605, and a package 606. The substrate 601 has the above-describedrectifier circuit, demodulation circuit, logic circuit, modulationcircuit, oscillator circuit, and the like. The substrate is preferably asingle-crystalline silicon substrate, a glass substrate, a plasticsubstrate, or the like, but the invention is not limited to this.

Although the antenna 602 is formed on the substrate 601, the position ofthe antenna 602 is not limited to this; it is also possible to provideanother substrate for forming the antenna 602. In addition, the ferrite603 is not necessarily required. However, in performing communicationwith a magnetic flux, using the ferrite 603 can improve the distributionof a magnetic flux and thus can enhance sensitivity. Although alithium-ion secondary button battery or the like is suitable for thesecondary battery 604, the battery is not limited to the lithium-ionbattery. Further, the shape of the battery is not limited to the button,and it is also possible to use a high-capacity capacitor such as anelectric double layer capacitor. The flexible printed board 605electrically connects the substrate 601 and the secondary battery 604.

The package 606 should be highly airtight on the assumption that thatthe package 606 is to be implanted in the body. In addition, the package606 should be formed from a material having no adverse effects on theliving body. In the case of using a secondary button battery, thepackage can be formed to a thickness of about 1 cm; thus, it can be evenswallowed by humans.

Such a highly airtight package cannot be opened frequently. Therefore,when a primary battery which is non-rechargeable is used, the sensordevice becomes inactive once the battery has run out. However, when asecondary battery which is wirelessly rechargeable is used as in theinvention, the sensor device can be used without concern for the chargedlevel of the battery. Further, even when the sensor device is locatedinside the body, the battery can be recharged from outside of the body.

Thus, using the wireless sensor device of the invention can acquirephysical information by radio communication.

[Embodiment 2]

Embodiment 2 of the invention is shown in FIG. 7. FIG. 7 illustrates across section of the wireless sensor device of the invention. Thewireless sensor device shown in FIG. 7 includes the substrate 601, theantenna 602, the ferrite 603, the secondary battery 604, the flexibleprinted board 605, the package 606, an LED 607, a CCD 608, and a lens609. The substrate 601 has the above-described rectifier circuit,demodulation circuit, logic circuit, modulation circuit, oscillatorcircuit, and the like. The substrate is preferably a single-crystallinesilicon substrate, a glass substrate, a plastic substrate, or the like,but the invention is not limited to this.

Although the antenna 602 is formed on the substrate 601, the position ofthe antenna 602 is not limited to this; it is also possible to provideanother substrate for forming the antenna 602. In addition, the ferrite603 is not necessarily required. However, in performing communicationwith a magnetic flux, using the ferrite 603 can improve the distributionof a magnetic flux and thus can enhance sensitivity. Although alithium-ion secondary button battery is suitable for the secondarybattery 604, the battery is not limited to the lithium-ion battery.Further, the shape of the battery is not limited to the button, and itis also possible to use a high-capacity capacitor such as an electricdouble layer capacitor. The flexible printed board 605 electricallyconnects the substrate 601 to the secondary battery 604, the CCD 608,and the LED 607.

In the wireless sensor device of this embodiment, the LED 607 is lit toilluminate inside of the body. Then, the CCD 608 shoots an image of theilluminated object through the lens 609. The data shot is transmitted tothe substrate 601 through the flexible printed board 605, so that thedata is processed and wirelessly transmitted to outside of the body.

The package 606 should be highly airtight on the assumption that thepackage 606 is to be implanted in the body. In addition, a portion ofthe package 606 on the periphery of the LED 607 and the lens 609 shouldbe transparent to enable shooting. Further, the package 606 should beformed from a material having no adverse effects on the living body. Inthe case of using a secondary button battery, the package can be formedto a thickness of about 1 cm; thus, it can be even swallowed by humans.

Such a highly airtight package cannot be opened frequently. Therefore,when a primary battery which is non-rechargeable is used, the sensordevice becomes inactive once the battery has run out. However, when asecondary battery which is wirelessly rechargeable is used as in theinvention, the sensor device can be used without concern for the chargedlevel of the battery. Further, even when the sensor device is locatedinside the body, the battery can be recharged from outside of the body.This advantageous effect can be multiplied particularly in the case ofmounting a high-power-consumption element such as an LED.

Thus, using the wireless sensor device of the invention can read outphysical information by radio communication.

This embodiment can be implemented in combination with any of EmbodimentModes 1 to 3 and Embodiment 1.

[Embodiment 3]

Embodiment 3 of the invention is shown in FIG. 8. FIG. 8 illustrates across section of the wireless sensor device of the invention. Thewireless sensor device shown in FIG. 8 includes the substrate 601, theantenna 602, the ferrite 603, a thin-film secondary battery 801, theflexible printed board 605, and the package 606. The substrate 601 hasthe above-described rectifier circuit, demodulation circuit, logiccircuit, modulation circuit, oscillator circuit, and the like. Thesubstrate is preferably a single-crystalline silicon substrate, a glasssubstrate, a plastic substrate, or the like, but the invention is notlimited to this.

Although the antenna 602 is formed on the substrate 601, the position ofthe antenna 602 is not limited to this; it is also possible to provideanother substrate for forming the antenna 602. In addition, the ferrite603 is not necessarily required.

However, in performing communication with a magnetic flux, using theferrite 603 can improve the distribution of a magnetic flux and thus canenhance sensitivity. A thin-film lithium-ion secondary battery is usedfor the thin-film secondary battery 801. When such a thin-filmlithium-ion battery is used, the thickness of the secondary battery canbe made 1 mm or less. The flexible printed board 605 electricallyconnects the substrate 601 and the thin-film secondary battery 801. Thewireless sensor device of this embodiment can be formed to have a totalthickness of 2 mm or less, whereby it can be implanted even under theskin of a human body.

The package 606 should be highly airtight on the assumption that thatthe package 606 is to be implanted in the body. However, such a highlyairtight package cannot be opened frequently. Therefore, when a primarybattery which is non-rechargeable is used, the sensor device becomesinactive once the battery has run out. However, when a secondary batterywhich is wirelessly rechargeable is used as in the invention, the sensordevice can be used without concern for the charged level of the battery.Further, even when the sensor device is located inside the body, thebattery can be recharged from outside of the body.

Thus, using the wireless sensor device of the invention can acquirephysical information by radio communication.

This embodiment can be implemented in combination with any of EmbodimentModes 1 to 3 and Embodiments 1 and 2.

[Embodiment 4]

Embodiment 4 of the invention is shown in FIG. 9. FIG. 9 is a top viewof a substrate provided with circuits. For the substrate 601, asingle-crystalline silicon substrate, a glass substrate, a plasticsubstrate, or the like can be used, but the invention is not limited tothis.

Circuits 901 to 906 represent circuits formed over the substrate 601.The circuits 901 to 906 include, for example, the oscillation circuit,the modulation circuit, the demodulation circuit, the logic circuit, theAD converter circuit, the sensor circuit, the memory circuit, therectifier circuit, the charging circuit or the stabilizing power supplycircuit, and the like that are shown in FIG. 1. The antenna 602 isformed over the circuits 901 to 906. The flexible printed board 605 forconnection with a battery such as a secondary battery or an electricdouble layer capacitor is electrically connected to the circuits 901 to906 over the substrate 601.

This embodiment can be implemented in combination with any of EmbodimentModes 1 to 3 and Embodiments 1 to 3.

[Embodiment 5]

Embodiment 5 of the invention is shown in FIG. 12. FIG. 12 illustrates across-sectional view of a thin-film secondary battery. Hereinafter,description will be given of the thin-film secondary battery used inEmbodiment 3. Secondary batteries include nickel-cadmium batteries,lithium-ion batteries, lead batteries, and the like. Among them,lithium-ion batteries, which have no memory effects and can discharge alarge amount of current, have been widely used.

In recent years, research has been conducted on fabrication of thinnerlithium-ion batteries. Among them, there has emerged a lithium-ionbattery having a thickness of one to several pm. Such a thin-filmsecondary battery can be used as a flexible secondary battery.

First, a current-collecting thin film 7102 to serve as an electrode isformed over a substrate 7101. The current-collecting thin film 7102should have high adhesion to an upper negative electrode active materiallayer 7103 and have low resistance. Specifically, aluminum, copper,nickel, vanadium, or the like can be used for the current-collectingthin film 7102.

Next, the negative electrode active material layer 7103 is formed overthe current-collecting thin film 7102. Generally, vanadium oxide or thelike is used for the negative electrode active material layer 7103.Next, a solid electrolyte layer 7104 is formed over the negativeelectrode active material layer 7103. Generally, lithium phosphate orthe like is used for the solid electrolyte layer 7104. Next, a positiveelectrode active material layer 7105 is formed over the solidelectrolyte layer 7104. Generally, lithium manganate or the like is usedfor the positive electrode active material layer 7105. Lithium cobaltateor lithium nickel oxide may also be used. Next, a current-collectingthin film 7106 to serve as an electrode is formed over the positiveelectrode active material layer 7105. The current-collecting thin film7106 should have high adhesion to the positive electrode active materiallayer 7105 and have low resistance. For example, aluminum, copper,nickel, vanadium, or the like can be used. Each layer may be formed byusing either a sputtering technique or an evaporation technique. Inaddition, the thickness of each layer is preferably 0.1 to 3 μm.

Next, charging and discharging operations will be described. In chargingthe battery, lithium ions are desorbed from the positive electrodeactive material layer 7105. Then, the lithium ions are absorbed into thenegative electrode active material layer 7103 through the solidelectrolyte layer 7104. At this time, electrons are released to outsidefrom the positive electrode active material layer 7105. In dischargingthe battery, on the other hand, lithium ions are desorbed from thenegative electrode active material layer 7103. Then, the lithium ionsare absorbed into the positive electrode active material layer 7105through the solid electrolyte layer 7104. At this time, electrons arereleased to outside from the negative electrode active material layer7103. The thin-film secondary battery operates in this manner. With sucha thin-film secondary battery, a compact and lightweight battery can beconstructed.

This embodiment can be implemented in combination with any of EmbodimentModes 1 to 3 and Embodiments 1 to 4.

[Embodiment 6]

Embodiment 6 of the invention is shown in FIGS. 10A to 11B. Thisembodiment will describe an electric double layer capacitor. Thestructure of the electric double layer capacitor is shown in FIG. 10A.

Two electrodes (a positive electrode 1001 and a negative electrode 1002)are put in an electrolyte 1004, and a voltage is applied across the twoelectrodes. A separator 1003 is disposed between the positive electrode1001 and the negative electrode 1002 so that these electrodes are notshorted in the electrolyte. Generally, the electrolyte 1004 starts to beelectrolyzed at a voltage of about 1 V so that a current flows betweenthe electrodes, although the voltage level differs depending on the kindof the electrolyte 1004. However, when the voltage across the twoelectrodes is low, electrolysis reaction does not occur. At this time, alayer of polarized ions 1005 is formed around the electrodes as shown inFIG. 10A. Such layer of the polarized ions 1005 is referred to as anelectric double layer, and can be used as a capacitor 1006 as shown inFIG. 10B. A capacitor using an electric double layer has the followingfeatures.

The layer of the polarized ions is very thin. Therefore, when anelectrode with a large surface area is prepared, a capacitor with a highcapacitance value can be formed. The thinnest electric double layer isas thin as one molecule.

In order to prepare an electrode with a large surface area, activatedcarbon 1101 is attached to the surfaces of the positive electrode 1001and the negative electrode 1002 as shown in FIG. 11A, so that thesurface of the activated carbon is also used as the electrode. Having alarge surface area, the activated carbon 1101 is effective for formingan electric double layer with a large area. A magnified view of theactivated carbon 1101 is shown in FIG. 11B. The polarized ions 1005 areformed on the surface of the activated carbon 1101, thereby functioningas the capacitor 1006. Such a capacitor 1006 can function as a capacitoronly at a voltage lower than the voltage level at which electrolysisreaction occurs, and has a disadvantage in low withstand voltage.However, when such an electric double layer capacitor is used, it ispossible to obtain a capacitor with a small volume and a highcapacitance value. Specifically, a capacitor of 0.1 F or more, which hasa size of about a coin, can be obtained.

This embodiment can be implemented in combination with any of EmbodimentModes 1 to 3 and Embodiments 1 to 5.

[Embodiment 7]

Embodiment 7 of the invention is shown in FIGS. 13A and 13B. FIGS. 13Aand 13B illustrate specific examples of a photosensor.

FIG. 13A is a cross-sectional view of a photosensor. The photosensor ofthis embodiment uses a PIN diode. First, a transparent conductive film1302 is formed over a substrate 1301. Then, p-type amorphous silicon1303, i-type amorphous silicon 1304, n-type amorphous silicon 1305, andan electrode 1306 are sequentially formed and patterned intopredetermined shapes. Then, an interlayer film 1309 is formed andcontact holes are formed in the interlayer film 1309 so as to partiallyexpose the transparent conductive film 1302 and the electrode 1306.Then, an electrode 1308 connected to the transparent conductive film1302 at the contact hole as well as an electrode 1307 connected to theelectrode 1306 at the contact hole are formed.

FIG. 13B shows a connection relation between the photosensor and otherelements in a sensor circuit. A resistor 1311 is connected to a PINdiode 1310 and a reverse-bias voltage is applied to the PIN diode 1310by a power supply 1312. When the PIN diode 1310 receives light, aphotocurrent flows through the PIN diode 1310, and a voltage Vr isgenerated across opposite terminals of the resistor 1311. By reading outthis voltage Vr, the amount of light can be detected.

This embodiment can be implemented in combination with any of EmbodimentModes 1 to 3 and Embodiments 1 to 6.

[Embodiment 8]

Embodiment 8 of the invention is shown in FIG. 14. FIG. 14 illustratesan example of a pressure sensor. The pressure sensor of this embodimentincludes resistors formed from semiconductors (semiconductor resistors)1401 to 1404, a differential amplifier 1405, power supply terminals 1406and 1407, and an output terminal 1408.

The resistors 1401 and 1402 are connected in series between the powersupply terminals 1406 and 1407. Similarly, the resistors 1403 and 1404are connected in series between the power supply terminals 1406 and1407. The resistors 1401 and 1402 are connected in parallel with theresistors 1403 and 1404. The resistors 1401 and 1402 are connected tothe differential amplifier 1405 such that a potential between theresistors 1401 and 1402 is input to a non-inverting input terminal (+)of the differential amplifier 1405. Similarly, the resistors 1403 and1404 are connected to the differential amplifier 1405 such that apotential between the resistors 1403 and 1404 is input to an invertinginput terminal (−) of the differential amplifier 1405.

The resistance value of a normal semiconductor resistor changes inresponse to pressure applied, due to a piezoelectric effect. Whenpressure is applied to the pressure sensor of this embodiment, pressureswith different levels are applied to the resistors 1401 and 1404. Uponapplication of pressure, potentials input to the inverting inputterminal (−) and the non-inverting input terminal (+) of thedifferential amplifier change. By amplifying the potential difference,the presence of pressure can be detected. When this pressure sensor isused for the above-described wireless sensor device, informationacquired by the sensor circuit can be transmitted as radio waves.

Note that a pressure sensor used in the invention is not limited to theconfiguration shown in this embodiment, and a circuit with a differentstructure may be used.

As described above, the applicable range of the invention is so widethat it can be applied to any wireless sensor device which transmitsinformation that is sensed. In addition, this embodiment can beimplemented in combination with any of Embodiment Modes 1 to 3 andEmbodiments 1 to 7.

[Embodiment 9]

Next, a method of fabricating the wireless sensor device of theinvention will be described in detail. Although this embodimentillustrates a thin film transistor (TFT) as an exemplary semiconductorelement, a semiconductor element used in the wireless sensor device ofthe invention is not limited to this. For example, not only a TFT butalso a memory element, a diode, a resistor, a coil, a capacitor, aninductor, or the like can be used.

This embodiment will describe an example where the thin-film secondarybattery shown in Embodiment 5 is used as a battery, and an antenna, thebattery, and a semiconductor element are all formed over the samesubstrate. When the antenna, the battery, and the semiconductor elementare all formed over the same substrate, a compact wireless sensor devicecan be provided. Note that the invention is not limited to thisstructure, and it is also possible to separately form an antenna or abattery and a semiconductor element, and electrically connect themafterwards.

First, as shown in FIG. 15A, an insulating film 701, a release layer702, an insulating film 703 functioning as a base film, and asemiconductor film 704 are sequentially formed over a heat-resistantsubstrate 700. The insulating film 701, the release layer 702, theinsulating film 703, and the semiconductor film 704 can be formed insuccession.

For the substrate 700, it is possible to use, for example, a glasssubstrate made of barium borosilicate glass, aluminoborosilicate glass,or the like; a quartz substrate; a ceramic substrate; or the like. It isalso possible to use a metal substrate such as a stainless steelsubstrate or a semiconductor substrate such as a silicon substrate. Asubstrate made of a flexible synthetic resin, e.g., plastic generallyhas a lower allowable temperature limit than the above-describedsubstrates; however, such substrate can be used as long as it canwithstand the processing temperature in the fabrication process.

Examples of a plastic substrate include polyester typified bypolyethylene terephthalate (PET), polyethersulfone (PES), polyethylenenaphthalate (PEN), polycarbonate (PC), nylon, polyetheretherketone(PEEK), polysulfone (PSF), polyetherimide (PEI), polyarylate (PAR),polybutylene terephthalate (PBT), polyimide,acrylonitrile-butadiene-styrene resin, polyvinyl chloride,polypropylene, polyvinyl acetate, acrylic resin, and the like.

Although the release layer 702 is provided over the entire surface ofthe substrate 700 in this embodiment, the invention is not limited tothis structure. For example, the release layer 702 may be formedpartially over the substrate 700 by a photolithography method or thelike.

The insulating films 701 and 703 are formed by depositing an insulatingmaterial such as silicon oxide, silicon nitride (e.g., SiN_(x) orSi₃N₄), silicon oxynitride (SiO_(x)N_(y) where x>y>0), or siliconnitride oxide (SiN_(x)O_(y) where x>y>0) by a CVD method, a sputteringmethod, or the like.

The insulating films 701 and 703 are provided to prevent an alkali metalsuch as Na or an alkaline earth metal contained in the substrate 700from being diffused into the semiconductor film 704, which wouldotherwise adversely affect the characteristics of semiconductor elementssuch as TFTs. In addition, the insulating film 703 functions to preventan impurity element contained in the release layer 702 from beingdiffused into the semiconductor film 704, and also functions to protectthe semiconductor elements in the later step of peeling thesemiconductor elements.

Each of the insulating films 701 and 703 can be either a singleinsulating film or stacked layers of a plurality of insulating films. Inthis embodiment, the insulating film 703 is formed by sequentiallydepositing a silicon oxynitride film to a thickness of 100 nm, a siliconnitride oxide film to a thickness of 50 nm, and a silicon oxynitridefilm to a thickness of 100 nm. However, the material and thickness ofeach film as well as the number of stacked layers are not limited tothis example. For example, the bottom silicon oxynitride film may bereplaced with a siloxane resin having a thickness of 0.5 to 3 μm that isformed by a spin coating method, a slit coating method, a dropletdischarge method, a printing method, or the like. In addition, themiddle silicon nitride oxide film may be replaced with a silicon nitride(e.g., SiN_(x) or Si₃N₄) film. Further, the top silicon oxynitride filmmay be replaced with a silicon oxide film. The thickness of each film ispreferably 0.05 to 3 μm, and can be freely selected within this range.

Alternatively, it is also possible to form the bottom layer of theinsulating film 703, which is closest to the release layer 702, using asilicon oxynitride film or a silicon oxide film, form the middle layerusing a siloxane resin, and form the top layer using a silicon oxidefilm.

Note that a siloxane resin is a resin formed from a siloxane material asa starting material and having the bond of Si—O—Si. A siloxane resin maycontain as a substituent at least one of fluorine, an alkyl group, andaromatic hydrocarbon, in addition to hydrogen.

The silicon oxide film can be formed by thermal CVD, plasma CVD,atmospheric pressure CVD, bias ECRCVD, or the like, using a mixed gas ofSiH₄/O₂, TE0S(tetraethoxysilane)/O₂, or the like. The silicon nitridefilm can be typically formed by plasma CVD using a mixed gas ofSiH₄/NH₃. The silicon oxynitride film and the silicon nitride oxide filmcan be typically formed by plasma CVD using a mixed gas of SiH₄/N₂O.

For the release layer 702, it is possible to use a metal film, a metaloxide film, or a stacked film of a metal film and a metal oxide film.The metal film and the metal oxide film can be either a single layer ora stacked structure of a plurality of layers. In addition to a metalfilm or a metal oxide film, metal nitride or metal oxynitride can alsobe used. The release layer 702 can be formed by a sputtering method orvarious CVD methods such as a plasma CVD method.

Examples of metals used for the release layer 702 include tungsten (W),molybdenum (Mo), titanium (Ti), tantalum (Ta), niobium (Nb), nickel(Ni), cobalt (Co), zirconium (Zr), zinc (Zn), ruthenium (Ru), rhodium(Rh), palladium (Pd), osmium (Os), iridium, and the like. In addition tosuch metal films, the release layer 702 can also be formed using a filmmade of an alloy containing the above-described metal as a maincomponent or a compound containing the above-described metal.

Alternatively, the release layer 702 can also be formed using a singlesilicon (Si) film or a film made of a compound containing silicon (Si)as a main component. As a further alternative, the release layer 702 canalso be formed using a film made of an alloy of silicon (Si) and theabove-described metal. A film containing silicon can have any ofamorphous, microcrystalline, and polycrystalline structures.

The release layer 702 can be either a single layer of theabove-described film or stacked layers thereof. The release layer 702having a stack of a metal film and a metal oxide film can be formed bysequentially forming a base metal film and oxidizing or nitriding thesurface of the metal film. Specifically, plasma treatment may be appliedto the base metal film in an oxygen atmosphere or an N₂O atmosphere, orthermal treatment may be applied to the metal film in an oxygenatmosphere or an N₂O atmosphere. Alternatively, oxidation can beaccomplished by forming a silicon oxide film or a silicon oxynitridefilm on the base metal film. Similarly, nitridation can be accomplishedby forming a silicon oxynitride film or a silicon nitride film on thebase metal film.

As the plasma treatment for oxidation or nitridation of the metal film,it is possible to perform high-density plasma treatment with a plasmadensity of 1×10¹¹ cm⁻³ or higher, preferably in the range of 1×10¹¹ to9×10¹⁵ cm ⁻³ and with high frequency such as microwaves (e.g., afrequency of 2.45 GHz).

Although the release layer 702 having a stack of a metal film and ametal oxide film can be formed by oxidizing the surface of the basemetal film, it is also possible to sequentially form a metal film andform a metal oxide film thereon.

For example, in the case of using tungsten as a metal, a tungsten filmis formed as a base metal film by a sputtering method, a CVD method, orthe like, and then plasma treatment is applied to the tungsten filmAccordingly, a tungsten film that is a metal film and a metal oxide filmthat is in contact with the metal film and is formed from oxide oftungsten can be formed.

Note that oxide of tungsten is given by WO_(x) where x is in the rangeof 2 to 3. There are cases where x is 2 (WO₂), x is 2.5 (W₂O₅), x is2.75 (W₄O₁₁), and x is 3 (WO₃). In formation of oxide of tungsten, thereis no limitation on the value of x, and the value of x may be determinedbased on the etching rate or the like.

It is preferable that the semiconductor film 704 be consecutively formedafter the formation of the insulating film 703 without exposure to air.The thickness of the semiconductor film 704 is 20 to 200 nm (preferably40 to 170 nm, or more preferably 50 to 150 nm). Note that thesemiconductor film 704 may be either an amorphous semiconductor or apolycrystalline semiconductor. Further, not only silicon but alsosilicon germanium can be used for the semiconductor. In the case ofusing silicon germanium, the concentration of germanium is preferablyabout 0.01 to 4.5 atomic %.

Note that the semiconductor film 704 can be crystallized by a knowntechnique. As a known crystallization method, there are a lasercrystallization method with laser light and a crystallization methodwith a catalytic element. Alternatively, it is also possible to combinea crystallization method with a catalytic element and a lasercrystallization method. In the case of using a thermally stablesubstrate such as quartz for the substrate 700, it is possible tocombine any of the following crystallization methods: a thermalcrystallization method with an electrically heated oven, a lamp annealcrystallization method with infrared light, a crystallization methodwith a catalytic element, and high temperature annealing at about 950°C.

For example, in the case of using laser crystallization, thermaltreatment at 550° C. is applied to the semiconductor film 704 for fourhours before the laser crystallization, in order to enhance theresistance of the semiconductor film 704 to laser. When acontinuous-wave solid-state laser is used and irradiation is conductedwith the second to fourth harmonics of the fundamental wave, crystalswith a large grain size can be obtained. Typically, the second harmonic(532 nm) or the third harmonic (355 nm) of an Nd:YVO₄ laser (thefundamental wave of 1064 nm) is preferably used. Specifically, laserlight emitted from a continuous-wave YVO₄ is converted into a harmonicwith a nonlinear optical element, so that laser light having an outputof 10 W is obtained. Then, the laser light is preferably shaped into arectangular shape or an elliptical shape with optics on the irradiationsurface. In this case, a laser power density of about 0.01 to 100 MW/cm²(preferably, 0.1 to 10 MW/cm²) is required, and irradiation is conductedwith a scanning rate of about 10 to 2000 cm/sec.

As a continuous-wave gas laser, an Ar laser, a Kr laser, or the like canbe used.

As a continuous-wave solid-state laser, the following can be used: a YAGlaser, a YVO₄ laser, a YLF laser, a YAlO₃ laser, a forsterite (Mg₂SiO₄)laser, a GdVO₄ laser, a Y₂O₃ laser, a glass laser, a ruby laser, analexandrite laser, a Ti:sapphire laser, and the like.

Alternatively, the following pulsed lasers can be used: an Ar laser, aKr laser, an excimer laser, a CO₂ laser, a YAG laser, a Y₂O₃ laser, aYVO₄ laser, a YLF laser, a YAlO₃ laser, a glass laser, a ruby laser, analexandrite laser, a Ti:sapphire laser, a copper vapor laser, and a goldvapor laser.

The repetition rate of pulsed laser light may be set at 10 MHz orhigher, so that laser crystallization can be performed with aconsiderably higher repetition rate than the normally used repetitionrates in the range of several ten to several hundred Hz. It is said thatit takes several ten to several hundred nsec for the semiconductor film704 to become completely solidified after being irradiated with pulsedlaser light. Therefore, by using laser light with the above-describedrepetition rate, the semiconductor film 704 can be irradiated with thenext laser pulse after it is melted by the previous laser light butbefore it becomes solidified. Accordingly, the solid-liquid interface ofthe semiconductor film 704 can be moved continuously and, thus, thesemiconductor film 704 having crystal grains that have grown in thescanning direction can be formed.

Specifically, it is possible to form an aggregation of crystal grainshaving a width of about 10 to 30 μm in the scanning direction and awidth of about 1 to 5 μm in the a direction perpendicular to thescanning direction. By forming single crystals with crystal grains thathave continuously grown in the scanning direction, it is possible toform the semiconductor film 704 having few crystal grains at least inthe channel direction of a TFT.

Note that laser crystallization can be performed by irradiation with afundamental wave of continuous-wave laser light and a harmonic ofcontinuous-wave laser light in parallel. Alternatively, lasercrystallization can also be performed by irradiation with a fundamentalwave of continuous-wave laser light and a harmonic of pulsed laser lightin parallel.

Note that laser irradiation can be performed in an inert gas atmospheresuch as a rare gas or a nitrogen gas. Accordingly, roughness of thesemiconductor surface by laser irradiation can be suppressed, andvariations in threshold voltage of TFTs resulting from variations ininterface state density can be suppressed.

By the above-described laser irradiation, the semiconductor film 704with enhanced crystallinity can be formed. Note that it is also possibleto use a polycrystalline semiconductor, which is formed by a sputteringmethod, a plasma CVD method, a thermal CVD method, or the like, for thesemiconductor film 704.

Although the semiconductor film 704 is crystallized in this embodiment,it is not necessarily required to be crystallized and can remain as anamorphous silicon film or a microcrystalline semiconductor film toproceed to the following process. A TFT formed using an amorphoussemiconductor or a microcrystalline semiconductor involves lessfabrication steps than TFTs formed using a polycrystallinesemiconductor. Therefore, it has an advantage of low cot and high yield.

Further, it is also possible to use a single-crystalline semiconductorfilm formed on an insulating film (SOI: Silicon on Insulator), which isformed by a bonding method or a SIMOX (Separation by IMplanted OXygen)method, for an active layer of a TFT.

An amorphous semiconductor can be obtained by decomposing a gascontaining silicon by glow discharge. Examples of a gas containingsilicon include SiH₄, Si₂H₆, and the like. The gas containing siliconmay be diluted with hydrogen or with hydrogen and helium.

Next, as shown in FIG. 15B, the semiconductor film 704 is patterned intopredetermined shapes, so that island-shaped semiconductor films 705 to709 are formed. Then, a gate insulating film 710 is formed so as tocover the island-shaped semiconductor films 705 to 709. The gateinsulating film 710 can be formed by depositing a film containingsilicon nitride, silicon oxide, silicon nitride oxide, or siliconoxynitride, either in a single layer or stacked layers by a plasma CVDmethod, a sputtering method, or the like. When the gate insulating film710 is formed to have stacked layers, it is preferable to form athree-layer structure in which a silicon oxide film, a silicon nitridefilm, and a silicon oxide film are sequentially stacked over thesubstrate 700.

The gate insulating film 710 can also be formed by oxidizing ornitriding the surfaces of the island-shaped semiconductor films 705 to709 by high-density plasma treatment. High-density plasma treatment isperformed by using, for example, a mixed gas of a rare gas such as He,Ar, Kr, or Xe; and oxygen, nitrogen oxide, ammonia, nitrogen, orhydrogen. When plasma is excited by introduction of microwaves, plasmawith a low electron temperature and high density can be generated. Whenthe surfaces of the semiconductor films are oxidized or nitrided byoxygen radicals (there may also be OH radicals) or nitrogen radicals(there may also be NH radicals) generated by such high-density plasma,an insulating film with a thickness of 1 to 20 nm, typically 5 to 10 nmis formed to be in contact with the semiconductor films. Such aninsulating film having a thickness of 5 to 10 nm is used as the gateinsulating film 710.

Oxidation or nitridation of the semiconductor films by theabove-described high-density plasma treatment proceeds by solid-phasereaction. Therefore, interface state density between the gate insulatingfilm and the semiconductor films can be suppressed quite low. Further,by directly oxidizing or nitriding the semiconductor films byhigh-density plasma treatment, variations in thickness of the insulatingfilm to be formed can be suppressed. Furthermore, in the case where thesemiconductor films have crystallinity and the surfaces of thesemiconductor films are oxidized by solid-phase reaction by high-densityplasma treatment, crystal grain boundaries can be prevented from beinglocally oxidized at a fast speed. Thus, a uniform gate insulating filmwith low interface state density can be formed. A transistor whose gateinsulating film partially or wholly includes an insulating film formedby high-density plasma treatment can have suppressed variations incharacteristics.

Next, as shown in FIG. 15C, a conductive film is formed over the gateinsulating film 710, and the conductive film is patterned intopredetermined shapes, so that gate electrodes 711 are formed above theisland-shaped semiconductor films 705 to 709. In this embodiment, thegate electrodes 711 are each formed by patterning two stacked conductivefilms. For the conductive films, metals such as tantalum (Ta), tungsten(W), titanium (Ti), molybdenum (Mo), aluminum (Al), copper (Cu),chromium (Cr), and niobium (Nb) can be used. Alternatively, an alloycontaining the above-described metal as a main component or a compoundcontaining the above-described metal can also be used. Further, it isalso possible to use a semiconductor, e.g., polycrystalline silicondoped with an impurity element such as phosphorus which imparts oneconductivity type to the semiconductor film.

In this embodiment, a tantalum nitride film or a tantalum (Ta) film isused as a first conductive film, and a tungsten (W) film is used as asecond conductive film. Besides the example shown in this embodiment,the following combinations of two conductive films can be given asalternative examples: a tungsten nitride film and a tungsten film, amolybdenum nitride film and a molybdenum film, an aluminum film and atantalum film, an aluminum film and a titanium film, and the like.Tungsten and tantalum nitride have high heat resistance. Therefore,after the formation of the two conductive films, they may be heated forthe purpose of thermal activation. Further, as other exemplarycombinations of two conductive films, it is also possible to use silicondoped with an n-type impurity and nickel silicide, silicon doped with ann-type impurity and tungsten silicide, and the like.

Although this embodiment illustrates the gate electrode 711 having twostacked conductive films, the invention is not limited to thisstructure. The gate electrode 711 may also be formed from a singleconductive film or more than two stacked conductive films. In the caseof using a three-layer structure in which more than two conductive filmsare stacked, it is preferable to form a stacked structure of amolybdenum film, an aluminum film, and a molybdenum film.

The conductive films can be formed by a CVD method, a sputtering method,or the like. In this embodiment, a first conductive film is formed to athickness of 20 to 100 nm and a second conductive film is formed to athickness of 100 to 400 nm.

Note that a resist mask used for the formation of the gate electrode 711may be replaced with a mask made of silicon oxide, silicon oxynitride,or the like. In that case, it is necessary to perform an additionalpatterning step for formation of a mask of silicon oxide, siliconoxynitride, or the like. However, since reduction in thickness of themask in etching is less than the case of using a resist, the gateelectrode 711 with a desired width can be formed. Alternatively, thegate electrode 711 can be selectively formed by a droplet dischargemethod without using a mask.

Note that a droplet discharge method means a method of forming apredetermined pattern by discharging or ejecting a droplet containing apredetermined composition from an orifice. An inkjet method is given asone example.

Next, the island-shaped semiconductor films 705 to 709 are doped with anelement which imparts n-type conductivity (typically, P (Phosphorus) orAs (Arsenic)) with the gate electrodes 711 as masks, so that theisland-shaped semiconductor films 705 to 709 contain the impurityelement at a low concentration (a first doping step). The conditions ofthe first doping step are as follows: a dosage of 1×10¹⁵ to 1×10¹⁹/cm³and an acceleration voltage of 50 to 70 keV. However, the invention isnot limited to such conditions. By this first doping step, doping isperformed through the gate insulating film 710, so that a pair of n-typelow concentration impurity regions 712 are formed in each of theisland-shaped semiconductor films 705 to 709. Note that the first dopingstep may be performed with the island-shaped semiconductor film 708,which is to be a p-channel TFT, covered with a mask.

Next, as shown in FIG. 15D, a mask 770 is formed so as to cover theisland-shaped semiconductor films 705 to 707 and 709 that are to ben-channel TFTs. Then, the island-shaped semiconductor film 708 is dopedwith an impurity element which imparts p-type conductivity (typically, B(boron)) with the mask 770 and the gate electrode 711 as masks, so thatthe island-shaped semiconductor film 708 contains the impurity elementat a high concentration (a second doping step). The conditions of thesecond doping step are as follows: a dosage of 1×10¹⁹ to 1×10²⁰/cm³ andan acceleration voltage of 20 to 40 keV. By this second doping step,doping is performed through the gate insulating film 710, so that a pairof p-type high concentration impurity regions 713 are formed in theisland-shaped semiconductor film 708.

Next, as shown in FIG. 16A, the mask 770 is removed by ashing or thelike, and an insulating film is formed so as to cover the gateinsulating film 710 and the gate electrodes 711. The insulating film isformed by depositing a silicon film, a silicon oxide film, a siliconoxynitride film, a silicon nitride oxide film, or a film containing anorganic material such as an organic resin, either in a single layer orstacked layers by a plasma CVD method, a sputtering method, or the like.In this embodiment, a silicon oxide film is formed to a thickness of 100nm by a plasma CVD method.

Next, the gate insulating film 710 and the insulating film are partiallyetched by anisotropic etching (mainly in the perpendicular direction).By this anisotropic etching, the gate insulating film 710 is partiallyetched to leave gate insulating films 714 that are partially formed overthe island-shaped semiconductor films 705 to 709. In addition, theinsulating film is also etched partially by the anisotropic etching, sothat sidewalls 715 having a contact with the side faces of the gateelectrodes 711 are formed. The sidewalls 715 are used as doping masksfor formation of LDD (Lightly Doped Drain) regions. In this embodiment,a mixed gas of CHF₃ and He is used as an etching gas. Note that the stepof forming the sidewalls 715 is not limited to this example.

Next, a mask is formed so as to cover the island-shaped semiconductorfilm 708 that is to be a p-channel TFT. Then, the island-shapedsemiconductor films 705 to 707 and 709 are doped with an impurityelement which imparts n-type conductivity (typically, P or As) by usingthe mask, the gate electrodes 711, and the sidewalls 715 as masks, sothat the island-shaped semiconductor films 705 to 707 and 709 containthe impurity element at a high concentration (a third doping step). Theconditions of the third doping step are as follows: a dosage of 1×10¹⁹to 1×10²⁰/cm³ and an acceleration voltage of 60 to 100 keV. By thisthird doping step, a pair of n-type high concentration impurity regions716 are formed in each of the island-shaped semiconductor films 705 to707 and 709.

Note that the sidewalls 715 function as masks later at the time offorming low concentration impurity regions or non-doped offset regionsbelow the sidewalls 715 by doping the semiconductor film with animpurity which imparts n-type conductivity so that the semiconductorfilm contains the impurity element at a high concentration. Therefore,in order to control the width of the low concentration impurity regionsor the non-doped offset regions, the size of the sidewalls 715 may becontrolled by appropriately changing the anisotropic etching conditionsfor the formation of the sidewalls 715 or the thickness of theinsulating film.

Next, the mask is removed by ashing or the like, and then the impurityregions may be activated by thermal treatment. For example, a siliconoxynitride film with a thickness of 50 nm may be formed first, followedby thermal treatment at 550° C. in a nitrogen atmosphere for four hours.

Alternatively, a silicon nitride film containing hydrogen may be formedfirst to a thickness of 100 nm, followed by thermal treatment at 410° C.in a nitrogen atmosphere for one hour so that the island-shapedsemiconductor films 705 to 709 are hydrogenated. As a furtheralternative, the island-shaped semiconductor films 705 to 709 may besubjected to thermal treatment at 300 to 450° C. in an atmospherecontaining hydrogen for one to 12 hours so as to be hydrogenated. Thethermal treatment can be performed by a thermal annealing method, alaser annealing method, an RTA method, or the like. By the thermaltreatment, not only hydrogenation but also activation of the impurityelement that has been added into the semiconductor films can beaccomplished. As an alternative method of hydrogenation, it is alsopossible to perform plasma hydrogenation (which uses hydrogen excited byplasma). By such hydrogenation step, dangling bonds can be terminatedwith thermally excited hydrogen.

By the series of the above-described steps, n-channel TFTs 717 to 720and a p-channel TFT 721 are formed.

Next, as shown in FIG. 16B, an insulating film 722 functioning as apassivation film is formed for protection of the TFTs 717 to 721.Although the insulating film 722 is not necessarily required, theprovision of the insulating film 722 can prevent intrusion of animpurity such as an alkali metal or an alkaline earth metal into theTFTs 717 to 721. Specifically, it is preferable to use silicon nitride,silicon nitride oxide, aluminum nitride, aluminum oxide, silicon oxide,silicon oxynitride or the like for the insulating film 722. In thisembodiment, a silicon oxynitride film with a thickness of about 600 nmis used for the insulating film 722. In this case, the above-describedhydrogenation step may be performed after the formation of this siliconoxynitride film.

Next, an insulating film 723 is formed over the insulating film 722 soas to cover the TFTs 717 to 721. For the insulating film 723, thermallystable organic materials such as polyimide, acrylic, benzocyclobutene,polyamide, or epoxy can be used. In addition to such organic materials,it is also possible to use a low-dielectric constant material (a low-kmaterial), a siloxane resin, silicon oxide, silicon nitride, siliconoxynitride, silicon nitride oxide, PSG (phosphosilicate glass), BPSG(borophosphosilicate), alumina, and the like. A siloxane resin maycontain as a substituent at least one of fluorine, an alkyl group, andaromatic hydrocarbon, in addition to hydrogen. Note that the insulatingfilm 723 can also be formed by stacking a plurality of insulating filmsmade of such materials.

A method for forming the insulating film 723 can be selected asappropriate according to a material used, e.g., a CVD method, asputtering method, a SOG method, spin coating, dipping, spray coating, adroplet discharge method (e.g., an inkjet method, screen printing,offset printing, or the like), a doctor knife, a roll coater, a curtaincoater, a knife coater, or the like.

Next, contact holes are formed in the insulating films 722 and 723 so asto partially expose the island-shaped semiconductor films 705 to 709.Then, conductive films 724 to 733 are formed so as to be in contact withthe island-shaped semiconductor films 705 to 709 through the contactholes. Although a mixed gas of CHF₃ and He is used as an etching gas forformation of the contact holes, the invention is not limited to this.

The conductive films 724 to 733 can be formed by a CVD method, asputtering method, or the like. Specifically, the conductive films 724to 733 can be formed using aluminum (Al), tungsten (W), titanium (Ti),tantalum (Ta), molybdenum (Mo), nickel (Ni), platinum (Pt), copper (Cu),gold (Au), silver (Ag), manganese (Mn), neodymium (Nd), carbon (C),silicon (Si), or the like. Alternatively, an alloy containing theabove-described metal as a main component or a compound containing theabove-described metal can also be used. The conductive films 724 to 733can be either a single layer of the above-described metal film or aplurality of stacked layers thereof.

As an example of an alloy containing aluminum as a main component, analloy which contains aluminum as a main component and contains nickelcan be given. Further, an alloy which contains aluminum as a maincomponent and contains nickel and one or both of carbon and silicon canalso be given. Aluminum and aluminum silicon, which have a lowresistance value and are inexpensive, are the most suitable materialsfor formation of the conductive films 724 to 733. In particular, when analuminum silicon (Al—Si) film is used, generation of hillocks in resistbaking can be suppressed more than the case of using an aluminum film,in patterning the conductive films 724 to 733. Further, instead ofsilicon (Si), about 0.5% Cu may be mixed into the aluminum film.

Each of the conductive films 724 to 733 is preferably formed to have astacked structure of, for example, a barrier film, an aluminum silicon(Al—Si) film, and a barrier film, or a stacked structure of a barrierfilm, an aluminum silicon (Al—Si) film, a titanium nitride film, and abarrier film. Note that a barrier film is, for example, a film formedfrom titanium, titanium nitride, molybdenum, molybdenum nitride, or thelike. When barrier films are formed to sandwich an aluminum silicon(Al—Si) film therebetween, generation of hillocks of aluminum oraluminum silicon can be prevented more effectively. In addition, when abarrier film made of titanium which is a high reducible element isformed, even when there are thin oxide films on the island-shapedsemiconductor films 705 to 709, the oxide films can be reduced bytitanium contained in the barrier film, whereby a favorable contactbetween the conductive films 724 to 733 and the island-shapedsemiconductor films 705 to 709 can be obtained. Further, it is alsopossible to stack a plurality of barrier films In that case, theconductive films 724 to 733 can each have a five-layer structure inwhich titanium, titanium nitride, aluminum silicon, titanium, andtitanium nitride are sequentially stacked.

Note that the conductive films 724 and 725 are connected to the highconcentration impurity regions 716 of the n-channel TFT 717. Theconductive films 726 and 727 are connected to the high concentrationimpurity regions 716 of the n-channel TFT 718. The conductive films 728and 729 are connected to the high concentration impurity regions 716 ofthe n-channel TFT 719. The conductive films 730 and 731 are connected tothe high concentration impurity regions 713 of the p-channel TFT 721.The conductive films 732 and 733 are connected to the high concentrationimpurity regions 716 of the n-channel TFI 720.

Next, as shown in FIG. 16C, an insulating film 734 is formed so as tocover the conductive films 724 to 733. Then, contact holes are formed inthe insulating film 734 so as to partially expose the conductive films724, 726, 728, and 733. Then, conductive films 735 to 738 are formed soas to be in contact with the conductive films 724, 726, 728, and 733,respectively at the contact holes. Any material that can be used for theconductive films 724 to 733 can be used as the material of theconductive films 735 to 738.

The insulating film 734 can be formed using an organic resin film, aninorganic insulating film, or a siloxane insulating film. Examples of anorganic resin film include acrylic, epoxy, polyimide, polyamide,polyvinyl phenol, benzocyclobutene, and the like. Examples of aninorganic insulating film include silicon oxide, silicon oxynitride,silicon nitride oxide, a film containing carbon typified by DLC(diamond-like carbon), and the like. Note that a mask used for formationof an opening through a photolithography method can be formed by adroplet discharge method or a printing method. A method of forming theinsulating film 734 can be selected as appropriate according to amaterial used, e.g., a CVD method, a sputtering method, a dropletdischarge method, a printing method, or the like.

Next, a conductive film 739 functioning as an antenna and conductivefilms 740 to 742 functioning as wires are formed so as to be in contactwith the conductive films 735 to 738. In this embodiment, the conductivefilms 737 and 739 are in contact. Similarly, the conductive films 735and 740 are in contact, the conductive films 736 and 741 are incontract, and the conductive films 738 and 742 are in contact.

The conductive films 739 to 742 can be formed using a metal such assilver (Ag), gold (Au), copper (Cu), palladium (Pd), chromium (Cr),platinum (Pt), molybdenum (Mo), titanium (Ti), tantalum (Ta), tungsten(W), aluminum (Al), iron (Fe), cobalt (Co), zinc (Zn), tin (Sn), ornickel (Ni). In addition to such metal films, the conductive films 739to 742 can also be formed using a film made of an alloy containing theabove-described metal as a main component or a compound containing theabove-described metal. The conductive films 739 to 742 can be either asingle layer of the above-described film or a plurality of stackedlayers thereof.

The conductive films 739 to 742 can be formed by a CVD method, asputtering method, a printing method such as screen printing or gravureprinting, a droplet discharge method, a dispensing method, a platingmethod, a photolithography method, an evaporation method, or the like.

In the case of using a screen printing method, for example, theconductive films 739 to 742 can be formed by selectively printing aconductive paste, in which conductive particles with a particle size ofseveral nm to several ten μm are dispersed in an organic resin, onto theinsulating film 734. The conductive particles can be formed using silver(Ag), gold (Au), copper (Cu), nickel (Ni), platinum (Pt), palladium(Pd), tantalum (Ta), molybdenum (Mo), tin (Sn), lead (Pb), zinc (Zn),chromium (Cr), titanium (Ti), or the like. In addition to such metals,the conductive particles can also be formed using an alloy containingthe above-described metal as a main component or a compound containingthe above-described metal. Further, it is also possible to use fineparticles of silver halide or dispersible nanoparticles. In addition, asan organic resin contained in the conductive paste, polyimide, asiloxane resin, an epoxy resin, a silicone resin, or the like can beused.

As exemplary alloys of the above-described metals, the followingcombinations can be given: silver (Ag) and palladium (Pd), silver (Ag)and platinum (Pt), gold (Au) and platinum (Pt), gold (Au) and palladium(Pd), and silver (Ag) and copper (Cu). Further, conductive particles ofcopper (Cu) coated with silver (Ag) can also be used, for example.

Note that the conductive films 739 to 742 are preferably formed by thesteps of extruding a conductive paste by a printing method or a dropletdischarge method, and baking the paste. For example, in the case ofusing conductive particles (e.g., a particle size of 1 to 100 nm)containing silver as a main component for the conductive paste, theconductive films 739 to 742 can be formed by baking the conductive pasteat a temperature in the range of 150 to 300° C. Baking may be performedeither by lamp annealing with an infrared lamp, a xenon lamp, a halogenlamp, or the like, or by furnace annealing with an electric furnace.Further, laser annealing with an excimer laser or an Nd:YAG laser mayalso be used. In addition, fine particles containing solder or lead-freesolder as a main component can also be used. In that case, it ispreferable to use fine particles with a particle size not greater than20 μm. Solder and lead-free solder have the advantage of low cost.

When a printing method or a droplet discharge method is used, theconductive films 739 to 742 can be formed without using an exposuremask. Further, when a droplet discharge method or a printing method isused, waste of materials due to etching can be prevented unlike aphotolithography method. Further, since an expensive exposure mask isnot required, the fabrication cost of the wireless sensor device can besuppressed.

Next, as shown in FIG. 17A, an insulating film 743 is formed over theinsulating film 734 so as to cover the conductive films 739 to 742.Then, contact holes are formed in the insulating film 743 so as topartially expose the conductive films 740 to 742 functioning as thewires. The insulating film 743 can be formed using an organic resinfilm, an inorganic insulating film, or a siloxane insulating film.Examples of an organic resin film include acrylic, epoxy, polyimide,polyamide, polyvinyl phenol, benzocyclobutene, and the like. Examples ofan inorganic insulating film include silicon oxide, silicon oxynitride,silicon nitride oxide, a film containing carbon typified by DLC(diamond-like carbon), and the like. Note that a mask used for formationof an opening through a photolithography method can be formed by adroplet discharge method or a printing method. A method of forming theinsulating film 743 can be selected as appropriate according to amaterial used, e.g., a CVD method, a sputtering method, a dropletdischarge method, a printing method, or the like.

Next, as shown in FIG. 17B, layers of from the insulating film 703 up tothe insulating film 743, which include semiconductor elements typifiedby TFTs and various conductive films, (hereinafter collectively referredto as an “element formation layer 744”) are peeled off the substrate700. In this embodiment, a first seat material 745 is bounded to asurface of the insulating film 743 of the element formation layer 744,and the element formation layer 744 is peeled off the substrate 700 byusing a physical force. The release layer 702 may partially remainwithout being entirely removed.

The above-described peeling step may be performed by a method of etchingthe release layer 702. In this case, a protective layer is formed so asto cover the conductive films 740 to 742 in order to protect part of theconductive films 740 to 742 that has been exposed by etching. Then, atrench is formed so as to partially expose the release layer 702. Thetrench is formed by dicing, scribing, laser (including UV light)processing, a photolithography method, or the like. The trench may bedeep enough to expose the release layer 702.

The protective layer can be formed with an epoxy resin, acrylate resin,a silicone resin, or the like that is soluble in water or alcohols. Forexample, the protective layer can be formed by the steps of applying awater-soluble resin (VL-WSHL10, product of Toagosei Co., Ltd.) to athickness of 30 μm by a spin coating method, pre-curing the resin bylight exposure for two minutes, and completely curing the resin by lightexposure again for 12.5 minutes in total (2.5 minutes from the rearsurface and 10 minutes from the front surface). In the case of stackinga plurality of organic resins, there is a possibility that part of theorganic resins might be melted or adhesion thereof might becomeextremely high during a coating step or a baking step depending on asolvent used. Therefore, in the case of using organic resins that aresoluble in the same solvent for the insulating film 743 and theprotective layer, it is preferable to form an inorganic insulating film(e.g., a silicon nitride film, a silicon nitride oxide film, an aluminumnitride film, or an aluminum nitride oxide film) so as to cover theinsulating film 743 in order that the protective layer can be smoothlyremoved in a subsequent step. After the formation of the protectivelayer, the release layer 702 is removed by etching. In this case,halogen fluoride is used as an etching gas, and the gas is introducedthrough the trench. In this embodiment, etching is performed under theconditions of, for example, using ClF₃ (chlorine trifluoride), atemperature of 350° C., a flow rate of 300 sccm, an atmospheric pressureof 6 Ton, and a period of three hours.

In addition, nitrogen may be mixed into the ClF₃ gas. Using halogenfluoride such as ClF₃ enables the release layer 702 to be selectivelyetched, so that the substrate 700 can be peeled off the TFTs 717 to 721.Note that halogen fluoride may be either gas or liquid.

Next, as shown in FIG. 18A, a second seat material 746 is attached to asurface of the element formation layer 744 that is exposed by theabove-described peeling step, and then the element formation layer 744is peeled off the first seat material 745. Then, conductive films 747 to749, which are connected to the conductive films 740 to 742,respectively through contact holes, are formed. In this embodiment, theconductive films 740 and 747 are in contact, the conductive films 741and 748 are in contact, and the conductive films 742 and 749 are incontact.

The conductive films 747 to 749 can be formed using metals such assilver (Ag), gold (Au), copper (Cu), palladium (Pd), chromium (Cr),platinum (Pt), molybdenum (Mo), titanium (Ti), tantalum (Ta), tungsten(W), aluminum (Al), iron (Fe), cobalt (Co), zinc (Zn), tin (Sn), andnickel (Ni). In addition to such metal films, the conductive films 747to 749 can also be formed using a film made of an alloy containing theabove-described metal as a main component or a compound containing theabove-described metal. The conductive films 747 to 749 can be either asingle layer of the above-described film or a plurality of stackedlayers thereof.

The conductive films 747 to 749 can be formed by a CVD method, asputtering method, a printing method such as screen printing or gravureprinting, a droplet discharge method, a dispensing method, a platingmethod, a photolithography method, an evaporation method, or the like.

Although this embodiment illustrates an example where the conductivefilms 747 to 749 are formed after peeling the element formation layer744 off the substrate 733, the formation of the conductive films 747 to749 may precede the peeling of the element formation layer 744 off thesubstrate 700.

Note that in the case where semiconductor elements corresponding to aplurality of wireless sensor devices are formed over the substrate 700,the element formation layer 744 is cut into individual wireless sensordevices. Cutting can be performed with a laser irradiation apparatus, adicing apparatus, a scribing apparatus, or the like. In this embodiment,a plurality of semiconductor elements formed over one substrate 700 arecut into corresponding wireless sensor devices by laser irradiation.

Next, a substrate 751 having a battery and a terminal for connecting asensor to a semiconductor element is prepared. This embodimentillustrates an example where a thin-film secondary battery 750 shown inEmbodiment 5 is used as a battery as shown in FIG. 18B.

Next, the structures of the thin-film secondary battery 750 and theterminal shown in FIG. 18B will be described. First, conductive films752 and 753 are formed over the substrate 751. The conductive film 752functions as a terminal for connecting a sensor to a semiconductorelement. The thin-film secondary battery 750 is formed over thesubstrate 751. Specifically, the thin-film secondary battery 750 has astructure in which a current-collecting thin film 754 connected to theconductive film 753, a negative electrode active material layer 755, asolid electrolyte layer 756, a positive electrode active material layer757, and a current-collecting thin film 758 are sequentially stackedover the substrate 751.

The current-collecting thin film 754 should have high adhesion to thenegative electrode active material layer 755 and have low resistance.For example, aluminum, copper, nickel, vanadium, gold, or the like ispreferably used for the current-collecting thin film 754. For thenegative electrode active material layer 755, vanadium oxide or the likeis generally used. For the solid electrolyte layer 756, lithiumphosphate, lithium phosphate doped with nitrogen, or the like isgenerally used. For the positive electrode active material layer 757,lithium manganate or the like is generally used. It is also possible touse lithium cobaltate or lithium nickel oxide for the positive electrodeactive material layer 757. The current-collecting thin film 758 shouldhave high adhesion to the positive electrode active material layer 757and have low resistance. For example, aluminum, copper, nickel,vanadium, gold, or the like can be used. Alternatively, thecurrent-collecting thin film 754 or 758 may also be formed using alight-transmissive conductive material such as ITO (Indium Tin Oxide).

Each of the above-described thin layers of the negative electrode activematerial layer 755, the solid electrolyte layer 756, the positiveelectrode active material layer 757, and the current-collecting thinfilm 758 may be formed by using either a sputtering method or anevaporation method. In addition, the thickness of each layer ispreferably 0.1 to 3 μm.

Next, an interlayer film 759 is formed using a resin. Then, theinterlayer film 759 is etched to form contact holes. The material of theinterlayer film 759 is not limited to a resin, and another film such asa CVD oxide film may also be used.

However, using a resin is preferable in terms of flatness. Further, aphotosensitive resin may also be used so that contact holes can beformed in the interlayer film 759 without etching. Next, conductivefilms 760 to 762 are formed over the interlayer film 759. The conductivefilm 760 is in contact with the conductive film 752 through the contacthole. The conductive film 761 is in contact with the current-collectingthin film 758 through the contact hole. By electrically connecting theconductive film 762 to the conductive film 753, electrical connection ofthe thin-film secondary battery 750 can be secured.

The conductive film 752 is connected to a conductive film 763 that isformed on an opposite surface (a second surface) to a surface (a firstsurface) of the substrate 751 having the conductive film 752, through acontact hole formed in the substrate 751. The contact hole in thesubstrate 751 may be formed by etching or laser ablation. In order tofacilitate the formation of the contact hole, the substrate 751 may bepolished and thinned by a CMP (Chemical-Mechanical Polishing) methodafter the formation of the conductive films 760 to 762. In thisembodiment, the conductive film 763 and the wire 764 connected to thesensor are electrically connected.

Next, as shown in FIG. 19, the conductive films 747 to 749 provided onthe element formation layer 744 and the conductive films 760 to 762 areelectrically connected. Specifically, the conductive film 747 and theconductive film 760 are electrically connected. In addition, theconductive film 748 and the conductive film 761 are electricallyconnected, and also the conductive film 749 and the conductive film 762are electrically connected.

This embodiment illustrates the case where the conductive films 747 to749 and the conductive films 760 to 762 are electrically connected bypressure bonding with an anisotropic conductive film (ACF), ananisotropic conductive paste (ACP), or the like. In this embodiment, anexample is shown in which connection is carried out with conductiveparticles 766 in an adhesive resin 765. Alternatively, connection mayalso be carried out with a conductive adhesive such as a silver paste, acopper paste, or a carbon paste, soldering, or the like.

Note that it is also possible to attach a third sheet material over thesubstrate 751 having the thin-film secondary battery 750 and the sensorelectrically connected to the conductive film 752, so that the secondseat material 746 and the third sheet material are bonded through one orboth of thermal treatment and pressure treatment. As the second sheetmaterial 746 and the third sheet material, hot-melt films and the likecan be used.

For the second sheet material 746 and the third sheet material, it ispossible to use a film on which antistatic treatment for preventingstatic electricity or the like has been applied (hereinafter referred toas an antistatic film). By sealing the device with antistatic films,semiconductor elements can be prevented from adverse effects such asexternal static electricity when dealt with as a commercial product.

Examples of an antistatic film include a film in which a material thatcan prevent electrostatic charge (an antistatic material) is mixed, afilm having an antistatic effect, a film coated with an antistaticagent, and the like. As an antistatic agent, the following can be used:nonionic polymers, anionic polymers, cationic polymers, a nonionicsurfactant, an anionic surfactant, a cationic surfactant, or anamphoteric surfactant. Alternatively, metals, indium tin oxide (ITO), orthe like can also be used as the antistatic agent. Exemplary materialsof a film having an antistatic effect include an olefin resin, an ABSresin, a styrene resin, a PMMA resin, a polycarbonate resin, a PVCpolyester resin, a polyamide resin, a modified PPO resin, and the like.

Although this embodiment has illustrated the example where a sensorwhich is separately prepared is electrically connected to thesemiconductor elements included in the element formation layer 744, theinvention is not limited to this structure. For example, the sensor maybe formed over the same substrate 700 as the semiconductor elements.

FIG. 23 illustrates the structure of the wireless sensor device of theinvention in which a photoelectric conversion element 767 is formed overthe substrate 700. Note that a sensor is not limited to thephotoelectric conversion element, and any of a resistor, an elementwhich uses capacitive coupling, an element which uses inducedelectromotive force, a photovoltaic element, a thermoelectric conversionelement, a transistor, a thermistor, a diode, and the like can be used.

Note that this embodiment can be implemented in combination with any ofEmbodiment Modes 1 to 3 and Embodiments 1 to 8.

[Embodiment 10]

This embodiment will describe an example where the wireless sensordevice of the invention is fabricated with transistors formed on asingle-crystalline substrate. Since transistors formed on asingle-crystalline substrate have small variations in characteristics,the number of transistors used for the wireless sensor device can besuppressed. In addition, this embodiment illustrates an example where athin-film secondary battery described in Embodiment 5 is used as abattery.

First, as shown in FIG. 20A, element-isolation insulating films 2301 forelectrically insulating semiconductor elements are formed usinginsulating films, over a semiconductor substrate 2300. The formation ofthe element-isolation insulating films 2301 allows a region 2302 forformation of transistors (an element formation region) and an elementformation region 2303 to be electrically insulated from each other.

The semiconductor substrate 2300 can be, for example, asingle-crystalline silicon substrate having n-type or p-typeconductivity, a compound semiconductor substrate (e.g., a GaAssubstrate, an InP substrate, a GaN substrate, a SiC substrate, asapphire substrate, or a ZnSe substrate), or the like.

The element-isolation insulating film 2301 can be formed by a LOCOS(LOCal Oxidation of Silicon) method, a trench isolation method, or thelike.

In this embodiment, an example is shown in which a single-crystallinesilicon substrate having n-type conductivity is used as thesemiconductor substrate 2300, and a p-well 2304 is formed in the elementformation region 2303. The p-well 2304 formed in the element formationregion 2303 of the semiconductor substrate 2300 can be formed byselectively doping the element formation region 2303 with an impurityelement which imparts p-type conductivity. As the impurity element whichimparts p-type conductivity, boron (B), aluminum (Al), gallium (Ga), orthe like can be used. In the case of using a semiconductor substratehaving p-type conductivity as the substrate 2300, an n-well region maybe formed by selectively doping the element formation region 2302 withan impurity element which imparts n-type conductivity.

Note that in this embodiment, the element formation region 2302 is notdoped with an impurity element because a semiconductor substrate havingn-type conductivity is used as the semiconductor substrate 2300.However, an n-well region may be formed in the element formation region2302 by doping the element formation region 2302 with an impurityelement which imparts n-type conductivity. As the impurity element whichimparts n-type conductivity, phosphorus (P), arsenic (As), or the likecan be used.

Next, as shown in FIG. 20B, insulating films 2305 and 2306 are formed soas to cover the element formation regions 2302 and 2303, respectively.In this embodiment, silicon oxide films formed in the element formationregions 2302 and 2303 by thermally oxidizing the semiconductor substrate2300 are used as the insulating films 2305 and 2306. Alternatively, itis also possible to use stacked layers of a silicon oxide film and asilicon oxynitride film, which are obtained by sequentially forming asilicon oxide film by thermal oxidation and forming a silicon oxynitridefilm thereon by nitriding the surface of the silicon oxide film bynitridation treatment, for the insulating films 2305 and 2306.

Further, as has been previously described, the insulating films 2305 and2306 may also be formed by plasma treatment. For example, by oxidizingor nitriding the surface of the semiconductor substrate 2300 byhigh-density plasma treatment, silicon oxide films or silicon nitridefilms to be used as the insulating films 2305 and 2306 can be formed inthe element formation regions 2302 and 2303, respectively.

Next, as shown in FIG. 20C, a conductive film is formed so as to coverthe insulating films 2305 and 2306. In this embodiment, an example isshown in which conductive films 2307 and 2308 that are sequentiallystacked are used. The conductive film may be either a single layer or astacked structure of more than two conductive films.

For the conductive films 2307 and 2308, metals such as tantalum (Ta),tungsten (W), titanium (Ti), molybdenum (Mo), aluminum (Al), copper(Cu), chromium (Cr), and niobium (Nb) can be used. In addition to suchmetal films, the conductive films 2307 and 2308 can also be formed usinga film made of an alloy containing the above-described metal as a maincomponent or a compound containing the above-described metal. Further,it is also possible to use a semiconductor, e.g., polycrystallinesilicon doped with an impurity element such as phosphorus which impartsone conductivity type to the semiconductor film. In this embodiment, theconductive film 2307 is formed using tantalum nitride and the conductivefilm 2308 is formed using tungsten.

Next, as shown in FIG. 21A, the stacked conductive films 2307 and 2308are patterned into predetermined shapes, whereby gate electrodes 2309and 2310 are formed over the insulating films 2305 and 2306,respectively.

Next, as shown in FIG. 21B, a resist mask 2311 is selectively formed soas to cover the element formation region 2302. Then, the elementformation region 2303 is doped with an impurity element. In doping theelement formation region 2303 with the impurity element, the gateelectrode 2310 as well as the mask 2311 functions as a mask. Therefore,impurity regions 2312 functioning as source and drain regions and achannel formation region 2313 are formed in the p-well 2304. As theimpurity element, an impurity element which imparts n-type conductivityor p-type conductivity is used. As the impurity element which impartsn-type conductivity, phosphorus (P), arsenic (As), or the like can beused. As the impurity element which imparts p-type conductivity, boron(B), aluminum (Al), gallium (Ga), or the like can be used. In thisembodiment, phosphorus (P) is used as the impurity element.

Next, the mask 2311 is removed, and a resist mask 2314 is selectivelyformed so as to cover the element formation region 2303, as shown inFIG. 21C. Then, the element formation region 2302 is doped with animpurity element. In doping the element formation region 2302 with theimpurity element, the gate electrode 2309 as well as the mask 2314functions as a mask. Therefore, impurity regions 2315 functioning assource and drain regions and a channel formation region 2316 are formedin the element formation region 2302 of the semiconductor substrate2300. As the impurity element, an impurity element which imparts n-typeconductivity or p-type conductivity is used. As the impurity elementwhich imparts n-type conductivity, phosphorus (P), arsenic (As), or thelike can be used. As the impurity element which imparts p-typeconductivity, boron (B), aluminum (Al), gallium (Ga), or the like can beused. In this embodiment, an impurity element (e.g., boron (B)) having adifferent conductivity type than the impurity element that has beenadded into the element formation region 2303 in FIG. 21B is used.

Next, as shown in FIG. 22A, an insulating film 2317 is formed so as tocover the insulating films 2305 and 2306 and the gate electrodes 2309and 2310. Then, contact holes are formed in the insulating film 2317 topartially expose the impurity regions 2312 and 2315. Next, conductivefilms 2318 which are connected to the impurity regions 2312 and 2315through the contact holes are formed. The conductive films 2318 can beformed by a CVD method, a sputtering method, or the like.

The insulating film 2317 can be formed using an inorganic insulatingfilm, an organic resin film, or a siloxane insulating film. Examples ofan inorganic insulating film include silicon oxide, silicon oxynitride,silicon nitride oxide, a film containing carbon typified by DLC(diamond-like carbon), and the like. Examples of an organic resin filminclude acrylic, epoxy, polyimide, polyamide, polyvinyl phenol,benzocyclobutene, and the like. A method of forming the insulating film2317 can be selected as appropriate according to a material used, e.g.,a CVD method, a sputtering method, a droplet discharge method, aprinting method, or the like.

Note that the structure of the transistors used in the wireless sensordevice of the invention is not limited to that shown in this embodiment.For example, an inversely staggered structure may be used.

Next, as shown in FIG. 22B, a thin-film secondary battery 2319 isformed. The thin-film secondary battery 2319 in this embodiment has astructure in which the conductive film 2318 serving as acurrent-collecting thin film, a negative electrode active material layer2320, a solid electrolyte layer 2321, a positive electrode activematerial layer 2322, and a current-collecting thin film 2323 aresequentially stacked. Note that the conductive film 2318 should havehigh adhesion to the negative electrode active material layer 2320 andhave low resistance, because part of the conductive film 2318 is used asthe current-collecting thin film in this embodiment. The conductive film2318 is preferably formed using aluminum, copper, nickel, vanadium,gold, or the like.

The structure of the thin-film secondary battery 2319 will now bedescribed in detail. In the thin-film secondary battery 2319, thenegative electrode active material layer 2320 is formed over theconductive film 2318. Generally, vanadium oxide or the like is used forthe negative electrode active material layer 2320. Next, a solidelectrolyte layer 2321 is formed over the negative electrode activematerial layer 2320. Generally, lithium phosphate, lithium phosphatedoped with nitrogen, or the like is used. Next, the positive electrodeactive material layer 2322 is formed over the solid electrolyte layer2321. Generally, lithium manganate or the like is used. Lithiumcobaltate or lithium nickel oxide may also be used. Then, thecurrent-collecting thin film 2323 to serve as an electrode is formedover the positive electrode active material layer 2322. Thecurrent-collecting thin film 2323 should have high adhesion to thepositive electrode active material layer 2322 and have low resistance.For example, aluminum, copper, nickel, vanadium, gold, or the like canbe used.

Alternatively, the conductive film 2318 or the current-collecting thinfilm 2323 may also be formed using a light-transmissive conductivematerial such as ITO (Indium Tin Oxide).

Each of the above-described thin layers of the negative electrode activematerial layer 2320, the solid electrolyte layer 2321, the positiveelectrode active material layer 2322, and the current-collecting thinfilm 2323 may be formed by using either a sputtering method or anevaporation method. In addition, the thickness of each layer ispreferably 0.1 to 3 μm.

Next, an interlayer film 2324 is formed using a resin. Then, theinterlayer film 2324 is etched to form contact holes. The material ofthe interlayer film is not limited to a resin, and another film such asa CVD oxide film may also be used. However, using a resin is preferablein terms of flatness. Further, a photosensitive resin may also be usedso that contact holes can be formed without etching. Next, wire layers2325 and 2326 are formed over the interlayer film. By connecting thewire layer 2325 and the conductive film 2318, electrical connection ofthe thin-film secondary battery 2319 is secured. Further, by connectingthe wire layer 2326 and the conductive film 2318, a sensor can beelectrically connected to the wire layer 2326.

Although this embodiment has illustrated the example where a sensorwhich is separately prepared is electrically connected to the wire layer2326, the invention is not limited to this structure. For example, thesensor may be formed over the semiconductor substrate 2300. In thiscase, the sensor can be formed using any of a resistor, an element whichuses capacitive coupling, an element which uses induced electromotiveforce, a photovoltaic element, a thermoelectric conversion element, aphotoelectric conversion element, a transistor, a thermistor, a diode,and the like.

By using the above-described fabrication method, the wireless sensordevice of the invention can have a structure in which a transistor isformed on a semiconductor substrate and a thin-film secondary battery isformed thereon. With such a structure, a wireless sensor device that isreduced in thickness and size can be provided.

Note that this embodiment can be implemented in combination with any ofEmbodiment Modes 1 to 3 and Embodiments 1 to 9.

The present application is based on Japanese Priority application No.2006-263752 filed on Sep. 28, 2006 with the Japanese Patent Office, theentire contents of which are hereby incorporated by reference.

1. (canceled)
 2. A device comprising: a positive electrode; and anegative electrode, wherein activated carbon is provided on a surface ofthe positive electrode and the negative electrode.
 3. A devicecomprising: a positive electrode; and a negative electrode, wherein eachof the positive electrode and the negative electrode comprises carbon.4. A device comprising: a positive electrode; and a negative electrode,wherein activated carbon is provided on a surface of the positiveelectrode and the negative electrode, and wherein polarized ions areprovided on a surface of the activated carbon.
 5. The device accordingto claim 2, wherein the positive electrode and the negative electrodefunction as capacitors.
 6. The device according to claim 3, wherein thepositive electrode and the negative electrode function as capacitors. 7.The device according to claim 4, wherein the polarized ions of one ofthe positive electrode and the negative electrode function as acapacitor.
 8. The device according to claim 4, wherein the polarizedions of one of the positive electrode and the negative electrodefunction as an electric double layer.
 9. The device according to claim5, wherein a capacitance of the capacitors are 0.1 F or more.
 10. Thedevice according to claim 6, wherein a capacitance of the capacitors are0.1 F or more.
 11. The device according to claim 7, wherein acapacitance of the capacitor is 0.1 F or more.
 12. The device accordingto claim 9, wherein a size of the capacitors is about a coin.
 13. Thedevice according to claim 10, wherein a size of the capacitors is abouta coin.
 14. The device according to claim 11, wherein a size of thecapacitor is about a coin.